Apparatus for Preventing Separation of Downhole Motor from Drillstring

ABSTRACT

A downhole motor for a drillstring has a housing with upper and lower portions coupled to one another. A rotor in the lower portion has an outward tapered receptacle at one end. An extension is coupled to the rotor and is disposed relative to a seat in the housing. An outer body of the extension has an external shoulder to engage the seat with separation of the upper and lower housing portions. An end of this outer body is disposed in the outward tapered receptacle of the rotor and defines an internal taper tapering inward in an internal passage of the body. An inner body is inserted into the internal passage of the outer body. An end of the inner body wedges the internal inward taper at the end of the outer body into the outward tapered receptacle on the rotor to hold the extension on the rotor. Should the lower housing portion separate from the upper housing portion, the shoulder on the extension can engage the seat so that the motor does not fully separate.

BACKGROUND OF THE DISCLOSURE

Drilling assemblies have downhole motors and other mechanisms to achieve directional drilling. Referring to FIG. 1A, for example, a drilling assembly 10 connects to a drillstring 14 and has a drill bit 12 rotatably connected to a downhole motor 20. A rig 16 at the surface can rotate the drillstring 14 and the assembly 10, and surface equipment 18 including mud pumps can pump drilling fluid or mud down the drillstring 14 to the downhole motor 20. Operated by the flow of drilling fluid, the downhole motor 20 can also impart rotation to the drill bit 12.

In general, the downhole motor 20 as shown in FIGS. 1A-1B has a housing 22, a power section 24, a transmission section 26, and a bearing section 28. Drilling fluid pumped through the motor 20 actuates the power section 24, which drives a mandrel 29 through the transmission section 26 to rotate the drill bit (12). The bearing section 28 supports the motor's drive mandrel 29.

The environment encountered by the downhole motor 20 is extremely hostile. For example, the motor 20 is continuously exposed to very high temperatures over very long periods of time. Therefore, the bearing section 28 in the motor 20 may occasionally fail, which prevents the free rotation of the drive mandrel 29 relative to the motor housing 22. When this occurs, portions of the motor housing 22 below the power section 24 tend to rotate with the rotational force applied by the power section 24 to the drill bit 12.

Should the bearings in the bearing section 28 cease to operate properly, for example, then the rotational force applied to the drill bit 12 is also applied to the motor housing 22. Eventually, portions of the motor's housing 22 can separate from one another, and portions of the motor 20 can possibly become lost in the well. Typically, the portions of the housing 22 are attached with right hand threads. Therefore, the clockwise rotation of the portions of the housing 22 relative to one another tends to unscrew sections of the housing 22 until they separate.

Apparatus for preventing separation of downhole motors has become standard equipment on directional drilling motors. One apparatus available in the art is disclosed in U.S. Pat. No. 5,165,492 by Dailey Petroleum Service Corp.

As an example, FIG. 1B shows one type of apparatus for preventing separation of the downhole motor 20 from the drillstring. The motor 20 has an upper housing member 30 coupled to a lower housing member 40 above the power section 24. A rotor extension 60 is coupled to the end of the rotor 44, which is disposed for rotation in the stator 42 of the power section 24. Should portions of the motor's housing 22 separate during operation, a head 62 on the end of the extension 60 can engage a seat 35 in the upper housing member 30 and can prevent the lower housing member 40 and/or other portions of the motor 20 from separating completely from the upper housing member 30 and drillstring.

Yet another apparatus is used in Weatherford's Hyperline Drilling Motor to prevent detachment of a drilling motor in the event of a housing separation. An example of this apparatus is illustrated in FIG. 2, which shows only an upper portion of a motor 20. Again, the motor 20 has an upper housing member 30 with a threaded end 34 coupled to a lower housing member 40. An upper threaded end 36 of the upper member 30 can affix to other tubular members of the drillstring (not shown). The lower housing member 40 supports a stator 42 with a rotor 44 disposed for rotation therein. Flow of drilling fluid in the space between the rotor 44 and stator 42 rotates the rotor 44, which in turn rotates a drill bit (not shown) further downhole on the motor 20.

The upper member 30 has an internal passage 32 separated at its upper end from the upper threads 36 by a reduced passage 35. The internal passage 32 at its lower end has internal threads 38 to which a seat 50 threads. A rotor extension 60 threads at one end 64 to the rotor 44, and the other end of the rotor extension 60 has a head 62, which positions within the internal passage 32.

Assembly of the apparatus involves separately affixing the components of the housing members 30 and 40, the seat 50, and the rotor extension 60 so that the rotor extension 60 can be held within the upper housing member 30. Should some lower housing portions of the motor 20 separate from one another, then the head 62 on the distal end of the rotor extension 60 can engage the seat 50 and prevent the lower components of the motor 20 from fully separating from the upper motor components and the drillstring.

Another apparatus is disclosed in U.S. Pat. No. 7,063,175 to Kerstetter, which is reproduced in FIG. 3. A retaining apparatus 70 is disposed on the end of a rotor 44 between upper and lower housing members 30 and 40 of a motor 20. The retaining apparatus 70 prevents separation and possible loss of the motor 20 and bit assembly due to decoupling of the housing members 30 and 40. A flange 55 having a central bore and a plurality of orifices is retained at a shoulder 45 between the housing members 30 and 40. A tubular collet 72 has a collar portion 74 at one end and has an upset portion 76 at the opposite end. The collet 72 passes through the central bore of the flange 55, and the upset portion 76 is attached to the rotor 44 by a tubular pin 80 extending longitudinally through the collet 72. The end of the rotor 44 is counter bored to receive the upset portion 76 of the collet 72 and tubular pin 80. To hold the pin 80 in place, threads 86 on the pin 80 thread inside the collet 72, while the end 88 of the pin 80 holds the upset portion 76 in the rotor's counter bore.

The separation catch mechanisms, such as discussed above, have performed adequately for many years. When the rotor catch is employed, however, the catch mandrel connection is exposed to reactive torques which can cause the connection to break-out, leading to loss of the drilling motor. For instance, the threaded connections of FIGS. 1B and 2 can back-off when engaged after housing disengagement.

Moreover, new developments in the power sections of motors and in the technology of drill bits have increased drilling rates by increasing the torque on the drill bit. These new developments have also been combined with changes to drilling practices, such as drilling both build and tangent sections of a borehole with a single motor bend setting (i.e., performing rotary drilling with significant bend in the motor). Under these conditions, the bending stiffness in the existing separation catch mechanisms may be imbalanced, which can result in connection fractures. In particular, the mechanism of FIG. 2 requires an excessively stiff pin end 34 due to the required step in the pin's internal dimension to accommodate the seat 50.

Finally, when the rotor catch is employed, the catch connection can also be exposed to vibrations and the like, which can cause the connection to break-out and can lead to loss of the drilling motor. The apparatus of FIG. 3 uses a tongue-in-groove, collet-style style connection, and the upset portion 76 makes up with a compressive fit. The extended pin 80 keeps the upset portion 76 from collapsing once installed, allowing axial load to be applied to the rotor 44. However, any vibration or radial loading can still allow the mandrel to work or wobble in the collet, which can cause the connection to break-out and can leading to loss of the drilling motor.

The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.

SUMMARY OF THE DISCLOSURE

According to the present disclosure, a downhole motor for a drillstring comprises a housing having upper and lower portions coupled to one another and having a seat disposed therein. The motor comprises a rotor disposed in the lower portion, and the rotor has an outward tapered receptacle at one end. The seat of the motor housing can be a separate landing shoulder fixedly installed in the upper portion. Alternatively, the set can be integrally formed in the upper portion.

An extension has a lower end coupled to the rotor and has an upper end disposed in the upper portion beyond the seat. The extension at least includes an outer body and an inner body. The outer body defines a first internal passage from a first end to a second end. The first end has an external shoulder disposed thereabout to engage the seat with separation of the upper and lower portions of the housing from one another. For its part, the second end is disposed in the outward tapered receptacle of the rotor and defines an internal taper tapering inward in the first internal passage.

The inner body has a third end and a fourth end. The inner body is inserted into the first internal passage of the outer body. The inner body's fourth end wedges the internal inward taper at the second end of the outer body into the outward tapered receptacle on the rotor.

The inner and outer bodies can be tubular. Also, the inner body can define a second internal passage from the third end to the fourth end, which can communicate with a through-bore of the rotor.

With the insertion of the inner body into the outer body, the third end of the inner body can have external thread threading with internal thread of the first internal passage at the first end of the outer body. Other forms of affixing can be used.

The internal inward taper of the second end of the outer body can include a conical wedge formed on the second end of the outer body. By the insertion of inner body into the outer body, this conical wedge can be expandable outward into the outward tapered receptacle on the rotor. To facilitate the expansion outward, the conical wedge can define a plurality of axial scores thereabout or can define a plurality of axial cuts thereabout forming a plurality of tabs.

The external shoulder disposed about the first end of the outer body can be an integrally formed shoulder or can have other configurations. For example, a tapered head on the first end of the outer body can have a ledge disposed thereabout. An expandable shoulder can be disposed on the tapered head against the ledge, and a nut can be tightened on the first end and can expand the expandable shoulder outward on the tapered head.

According to the present disclosure, an extension affixes to a receptacle on a distal end of a rotor for a downhole motor. The motor has a seat disposed in a housing between upper and lower portions coupled together. The extension includes an outer body and an inner body, such as discussed above.

According to the present disclosure, a method of assembling a downhole motor for a drillstring can be performed, not necessarily in the sequence provided. In the assembly, an upper portion of a motor housing couples to a lower portion of the motor housing. A lower end of an extension affixes to a receptacle on a distal end of a rotor disposed in the lower portion of the motor housing. To do this, a proximal end of an outer body of the extension inserts into the receptacle of the rotor, and an inner body inserts into the outer body toward an internal inward taper in a first internal passage of the outer body. The internal inward taper at the proximal end of the outer body wedges into the receptacle of the rotor with the inserted inner body. In the assembly, the upper end of the extension is arranged to engage relative to a seat in the motor housing with separation of the upper and lower portions from one another.

In the assembly, inserting the inner body into the outer body can involve threading external thread on the inner body to internal thread in the first internal passage of the outer body. Additionally, wherein wedging the internal inward taper at the proximal end of the outer body into the receptacle of the rotor with the inserted inner body can involve expanding a conical wedge, formed on the internal inward taper of the second end of the outer body, outward, by the inner body, into an outward taper of the receptacle on the rotor.

The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a drilling assembly disposed on a drillstring and having a downhole motor and a drill bit.

FIG. 1B illustrates a downhole motor in partial cross-section having one type of separation catch mechanism according to the prior art.

FIG. 2 illustrates another type of separation catch mechanism according to the prior art on the end of a rotor between upper and lower housing members of a motor.

FIG. 3 illustrates yet another type of separation catch mechanism according to the prior art on the end of a rotor between upper and lower housing members of a motor.

FIGS. 4A-4C illustrate a separation catch mechanism according to the present disclosure during a stage of assembly on the end of a rotor between upper and lower housing members of a motor.

FIGS. 4B-1 & 4C-1 show an alternative configuration for the end of the outer body.

FIGS. 4B-2 & 4C-2 show yet another configuration for the end of the outer body.

FIGS. 5A-5C illustrate the separation catch mechanism as assembled.

FIG. 6 illustrates another separation catch mechanism according to the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

As noted above, portions of a downhole motor can separate for a number of reasons during operation, such as when bearings in a bearing section of the motor fail. To deal with this potential separation, a separation catch mechanism 100 is used on a drilling motor 20 as shown in FIGS. 4A through 5C. In particular, FIGS. 4A-4C illustrate the separation catch mechanism 100 during a stage of assembly on the end of a rotor 44 between upper and lower housing members 30, 40 of the motor 20, whereas FIGS. 5A-5C illustrate the separation catch mechanism 100 as assembled.

Turning first to FIG. 4A, only portion of the downhole motor 20 is illustrated. The upper housing member 30 has a threaded pin end 34 that threads to the lower housing member 40 of the motor 20. An upper threaded box end 36 of the upper member 30 can affix to other tubular members of the drillstring (not shown). The lower member 40 supports a stator 42 with the rotor 44 disposed for rotation therein as part of the motor's power section. Although not shown, the motor 20 has other conventional components, such as a transmission section, bearing section, drive mandrel, etc.

During normal operation, the housing members 30 and 40 remain joined together to form a substantially unitary construction with a drilling fluid passage formed in the core thereof. Drilling fluid flows past the joint formed at the junction of the housing members 30 and 40. The flow of drilling fluid enters in the space between the stator 42 and the rotor 44, which rotates in the rotor 44 and in turn rotates a drill bit (not shown).

The upper member 30 may have an internal passage 32 separated at its upper end from the upper box end 36 by a reduced passage or throat 35. The internal passage 32 at its lower end has a seat 50. As shown, the seat 50 can be a separate flange, landing shoulder, or the like that fixedly installs inside the internal passage 32 in any number of suitable ways. Other types of seats 50 can be used, such as an integral seat formed inside the upper housing 30 in a manner similar to that disclosed later.

The catch mechanism 100 affixes at its lower end to the rotor 44, and an upper end of the extension 100 is disposed in the upper housing portion 40 beyond the seat 50. Should the housing members 30 and 40 separate, the catch mechanism 100 engages the seat 50 affixed to the upper housing member 30 so that the lower housing member 40 and related components are not lost.

The extension 100 includes inner and outer tubular bodies or pins 110, 120. For further reference, FIG. 4B shows an isolated view of the catch mechanism 100 during a stage of assembly on the end of the rotor 44, while FIG. 4C shows a detail of how the end of the catch mechanism 100 initially mates with the end of the rotor 44.

The catch mechanism 100 does not thread to the end of the rotor 44. Instead, the rotor 40 defines an outward tapered receptacle 102 that is smooth-walled and outward tapered (e.g., dovetailed), having a smaller inner dimension at the box face and a larger inner dimension at the back of the box end. The outer pin 110 inserts into the receptacle 102, and the inner pin 120 inserts and affixes inside the outer pin 110 to hold the outer pin 110 to the rotor 44.

In particular, the outer pin 110 defines a first internal passage 115 therethrough from a first end 111 a to a second end 111 b. The first end 111 a has an external shoulder 114 disposed thereabout to engage the seat 50 should the upper and lower portions 30, 40 of the housing separate from one another. The second end 111 b is disposed in the outward tapered receptacle 102 of the rotor 44.

The second end 111 b defines a plurality of tabs 112 formed by axial slots or cuts defined into the end 111 b that allow the tabs 112 to expand and contract for assembly and disassembly. Overall, the outer pin 110 has a straight outside diameter along its length. Internally, however, the inner passage 115 of the outer pin 110 defines a smooth, tapered inner dimension at the tabs 112 where the dimension at the pin face is smaller and tapers to the larger inner dimension of the tubular pin 110. In this way, the tabs 112 are inward-tapered or wedge-shaped, being fatter toward their distal ends than their proximal ends. Finally, the outer pin 110 contains a threaded box 116 at the top end 111 a to mate with the inner pin 120.

For its part, the inner pin 120 has a straight outer dimension and has external threads 126 at its upper end. The inner pin 120 is inserted into the first internal passage 115 of the outer pin 110 so that its threads 126 can thread with the internal threads 116 of the outer pin 110 and so its distal end 122 can wedge inside the tabs 112. As shown, the inner pin 120 can define a second internal passage 125 therethrough, which can be used for fluid communication, to conduct wires, etc.

To initially assemble the motor 20 and the catch mechanism 100, operators may thread the shoulder 50 in the pin end 34 of the upper housing 30 and may then thread the upper housing 30 to the lower housing 40, already having the rotor 44 and the stator 42. The catch mechanism 100 can then be inserted in the upper housing 30 and installed on the rotor 44. Other assembly methods can be used. For example, the separate seat 150 can fit around the mechanism 100, the mechanism 100 can be affixed to the rotor 44, and the seat 150 can be coupled to the upper housing 30. Finally, the two housings 30, 40 can be coupled together.

Either way, the end 111 b of the outer pin 110 is passed through the seat 50 and positioned in the receptacle 102 of the rotor 44. The inner pin 120 may already be partially installed in the outer pin 110 or may be inserted after the inner pin 120 has been inserted in the receptacle 102. Either way, the tabs 112 of the outer pin 110 are inserted all the way into the receptacle 102.

The operator then torques the inner pin 120 inside the outer pin 110, threading it inside the internal thread 116 at the upper end 111 a of the outer pin 110. Various tools can be used to achieve this. For example, a socket or other tool can be used to hold the outer pin 110, while another socket, Allen wrench, or the like is used to thread the inner tube 120 inside the outer tube 110.

During torqueing, the straight outer dimension 122 of the inner pin 120 passes into the tapered inner dimension of the outer pin 110, causing the dovetailed tabs 112 to expand into the mirrored taper of the receptacle 102. At the torqued state, the end 122 of the inner pin 120 makes up with the back of the tapered tabs 112, applying axial and radial compression to the connection.

Rather than having separate wedged tabs 112 on the second end 111 b of the outer body 110 formed by axial slots or cuts, the second end 111 b can have other configurations. As shown in FIGS. 4B-1 & 4C-1, for example, the internal taper tapering inward in the first internal passage 115 forming the conical wedge at the second end 111 b can merely have one or more axial scores 113 defined therein. These scores 113 are only partially defined in the surface of the outer body 110 to facilitate elastic expansion of the second end 111 b into the conical receptacle 102.

In another example shown in FIGS. 4B-2 & 4C-2, the internal taper tapering inward in the first internal passage 115 forming the conical wedge at the second end 111 b can lack any scores, cuts, or tabs. Instead, the conical wedge at this second end 111 b is elastically expandable outward by the inner body 120 into the outward tapered receptacle 102 on the rotor 44. As will be appreciated, these and other configurations can be used. As shown in FIGS. 5A-5C, the top end of the inner pin 110 affixes inside the first internal passage 115 of the outer pin 120, using the external thread 126 affixing to the internal thread 116 of the first internal passage 115. The straight end 122 of the inner pin 120 wedges the inward tapered tabs 112 at the second end 111 b of the outer pin 110 and forces them into the outward tapered receptacle 102 on the rotor 44. (Alternatively, in the other configurations noted above, the straight end 122 of the inner pin 120 can elastically expand the scored or unscored conical wedge at the second end 111 b of the outer pin 110 and wedge it into the outward tapered receptacle 102 on the rotor 44.)

As can be seen, the catch mechanism 100 uses the expandable dovetail connection with the dovetail tabs 112 fixing in the receptacle 102. When the connection is engaged, the inner pin 120 expands the dovetail tabs 112 in the inverse taper of the receptacle 102. This causes the two cone shapes to engage in compression along the full length of the taper. The compression is applied radially and axially when engaged. Having this level of compression within the connection can eliminate or reduce detrimental effects from vibration.

The extension 100 can transmit torque and is pre-loaded to prevent movement under vibration. In particular, the tab's faces are pre-loaded during assembly, making the connection less susceptible to possible movement under vibration. The dovetail connection provides high axial and radial compression to reduce vibration and encourage the mechanism 100 to act as a solid member with the rotor 44. In particular, force generated from vibration is directly related to centrifugal force generated from the mass of assembly 100. The outer pin 110 is the piece that will take most of the functional tension load. The inner pin 120 is required to add the compression load and takes primarily hoop compression. Given these stresses of the assembly 100, the materials used of outer pin 110 and inner pin 120 can be selected to optimize the mass to alter the centrifugal force generated from the mass of the assembly 100 and minimize the resulting vibrational force generated.

As noted above, clockwise rotation of the motor's housing components 30, 40 has a tendency to unscrew conventional right hand threads used to connect the components 30, 40 together. If rotation of the lower member 40 unscrews it from the upper member 30 or if some other motor housing components unscrew from one another, a longitudinal displacement occurs. Because the catch mechanism 100 is connected to the rotor 44, this longitudinal displacement moves the catch mechanism 100 to a seated position and can discontinue operation of the downhole motor 20.

In particular, should housing components 30, 40 separate on the motor 20, then the shoulder 114 on the top end of the catch mechanism 100 can engage the seat 50 and prevent the lower components of the motor 20 from fully separating from the upper components 30 and the drillstring.

The separation catch mechanism 100 can be beneficial in dealing with current challenges in motors (e.g., increased drilling rates, increased torque on the drill bit, drilling both build sections and tangent sections with a single motor bend setting, etc.). The dovetail connection provided by the mechanism 100 prevents axial separation when expanded and provides serviceability when collapsed. Additionally, the connection reduces the risk of failure due to a threaded connection break-out when torque is applied to the catch mechanism 100 during deployment.

The catch mechanism 100 provides axial constraint while allowing freedom in the rotational direction. If the drillstring is rotated after the safety catch of the shoulder 114 engages, the pins 110, 120 may spin, but the catch mechanism 100 can still axially support the motor 20. Only if the rotation is extreme, however, would the dovetail wedges of the tabs 112 be expected to unacceptably wear.

FIG. 6 illustrates another separation catch mechanism 100 according to the present disclosure. The catch mechanism 100 affixes at one end to the rotor 42 in a manner similar to that disclosed above. The other end of the catch mechanism 100 has a ledge 104, a conical surface or tapered head 106, and a threaded end 108, which position within the internal passage 32. An expandable shoulder 150, such as a washer, ring, or the like, is disposed on the tapered head 106 against the extension's ledge 104. A nut 152 tightened on the extension's threaded end 108 expands the shoulder 150 outward on the tapered head 106 and holds the shoulder 150 against the ledge 104.

As can be seen, the pin end 34 of the upper member 30 does not require internal threading to receive a seat as in the prior art. Instead, the upper housing 30 can have an integral shoulder or seat 130.

Assembly of the catch mechanism 100 involves assembling the expandable shoulder 150 on the tapered head 106 and threading the nut 152 hand-tight on the end 108 of the catch mechanism 100. With the nut 152 threaded only hand-tight, the shoulder's outside diameter is smaller than the internal diameter of the seat 130 toward the pin end 34 on the upper member 30. In this way, the end of the catch mechanism 100 can insert into the upper housing member 30.

A long wrench tool (not shown) is inserted through the box end 36 on the upper member 30 to engage the nut 152. Using a pipe wrench or the like, the exposed end of the catch mechanism 100 is gripped, and the nut 152 is tightened on the threaded end 108 to a specified torque. During tightening, the expandable shoulder 150 is pushed onto the tapered head 106, which increases the shoulder's outside diameter. At the torqued state, the expandable shoulder's outside diameter is bigger than the inside diameter of the seat 130. The expansion process can be controlled through the use of geometric features, such as grooves, slots, scores or the like, to separate the expandable shoulder 120 into a plurality of wedges, petals, or other shapes.

The rest of the downhole motor 20 and mechanism 100 can be assembled as before, and the assembly can be used downhole in a drilling operation. As noted above, clockwise rotation of the motor's housing components 30, 40 has a tendency to unscrew conventional right hand threads using to connect components of the motor 20 together. Thus, to prevent the catch mechanism 100 from being unscrewed from and separating from the downhole motor 20, left hand threads can be employed on the threaded portions of the catch mechanism 100.

If rotation of the lower member 40 unscrews it from the upper member 30 or if some other motor housing components unscrew from one another, a longitudinal displacement occurs. Because the catch mechanism 100 is connected to the rotor 44, this longitudinal displacement moves the catch mechanism 100 to a seated position and can discontinue operation of the downhole motor 20.

In particular, should housing components 30, 40 separate on the motor 20, then the expandable shoulder 150 on the distal end of the catch mechanism 100 can engage the seat 130 and prevent the lower components 40 of the motor 20 from fully separating from the upper components 30 and the drillstring.

The separation catch mechanism 100 minimizes changes to the stiffness at the pin end 34 of the upper housing member 30. This allows the bending stiffness between the pin end 34 and the box end 36 to be optimized. Having the pin end 34 with flexibility relative to the box end 36 can be beneficial in dealing with current challenges in motors (e.g., increased drilling rates, increased torque on the drill bit, drilling both build sections and tangent sections with a single motor bend setting, etc.).

Although the end of the catch mechanism 100 has been described above as having a ledge 104, a tapered head 106, and a threaded end 108 on which a nut 110 threads, a reverse arrangement could be used. Additional arrangements for the upper end of the catch mechanism 100 are disclosed in U.S. application Ser. No. 14/021,901, which is incorporated herein by reference.

The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. For example, although the present disclosure has disclosed that the separation catch mechanism is coupled to the rotor of a downhole motor's power section, it will be appreciated that the separation catch mechanism can be used above another type of downhole apparatus having a rotatable mandrel disposed in an outer housing. Additionally, although the wedge tabs 112 of the outer pin 110 have relatively smooth, outer sidewalls as do the inner surfaces of the receptacle 102, features for engagement can be included, such as serrations, teeth, ledges, shoulders, knurling, etc. Such features would allow insertion and removal of the tabs 112 into the receptacle 102, but may enhance the axial retention of the tabs 112 when wedged in the receptacle 102 by the inner pin 120.

It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter.

In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof. 

What is claimed is:
 1. A downhole motor for a drillstring, the motor comprising: a housing having upper and lower portions coupled to one another and having a seat; a rotor disposed in the lower portion and having an outward tapered receptacle at a distal end; and an extension having a lower end coupled to the rotor and having an upper end disposed in the upper portion beyond the seat, the extension at least including: an outer body defining a first internal passage from a first end to a second end, the first end having an external shoulder disposed thereabout to engage the seat with separation of the upper and lower portions of the housing from one another, the second end disposed in the outward tapered receptacle of the rotor and defining an internal taper tapering inward in the first internal passage; and an inner body having a third end and a fourth end, the inner body inserted into the first internal passage of the outer body, the fourth end wedging the internal inward taper at the second end of the outer body into the outward tapered receptacle on the rotor.
 2. The motor of claim 1, wherein the rotor defines a through-bore communicating with the outward tapered receptacle; and wherein the inner body defines a second internal passage from the third end to the fourth end, the second internal passage communicating with the through-bore of the rotor.
 3. The motor of claim 1, wherein the third end of the inner body comprises external thread threading to internal thread of the first internal passage at the first end of the outer body.
 4. The motor of claim 1, wherein the inner and outer bodies are tubular.
 5. The motor of claim 1, wherein the internal inward taper of the second end of the outer body comprises a conical wedge formed on the second end of the outer body, the conical wedge expandable outward, by the inner body, into the outward tapered receptacle on the rotor.
 6. The motor of claim 5, wherein the conical wedge defines a plurality of axial scores thereabout facilitating the expansion outward.
 7. The motor of claim 5, wherein the conical wedge defines a plurality of axial cuts thereabout forming a plurality of tabs.
 8. The motor of claim 1, wherein the external shoulder disposed about the first end of the outer body comprises: a tapered head on the first end having a ledge disposed thereabout; an expandable shoulder disposed on the tapered head against the ledge; and a nut tightened on the first end and expanding the expandable shoulder outward on the tapered head.
 9. The motor of claim 1, wherein the seat comprises a landing shoulder fixedly installed in the upper portion or integrally formed in the upper portion.
 10. An extension affixing to a receptacle on a distal end of a rotor for a downhole motor, the motor having a seat disposed in a housing between upper and lower portions coupled together, the extension comprising: an outer body defining a first internal passage from a first end to a second end, the first end having an external shoulder disposed thereabout to engage the seat with separation of the upper and lower portions of the housing from one another, the second end disposed in the receptacle of the rotor and defining an internal taper tapering inward in the first internal passage; and an inner body defining a second internal passage from a third end to a fourth end, the inner body inserted into the first internal passage of the outer body, the fourth end wedging the internal inward taper at the second end of the outer body into the receptacle of the rotor.
 11. The motor of claim 10, wherein the inner body defines a second internal passage therethrough from the third end to the fourth end.
 12. The motor of claim 10, wherein the third end of the inner body comprises external thread affixing to internal thread of the first internal passage at the first end of the outer body.
 13. The motor of claim 10, wherein the inner and outer bodies are tubular.
 14. The motor of claim 10, wherein the internal inward taper of the second end of the outer body comprises a conical wedge formed on the second end of the outer body, the conical wedge expandable outward by the inner body into the receptacle on the rotor.
 15. The motor of claim 14, wherein the conical wedge defines a plurality of axial scores thereabout facilitating the expansion outward.
 16. The motor of claim 14, wherein the conical wedge defines a plurality of axial cuts thereabout forming a plurality of tabs.
 17. The motor of claim 10, wherein the external shoulder disposed about the first end of the outer body comprises: a tapered head disposed on the first end and having a ledge disposed about the first end; an expandable shoulder disposed on the tapered head of the first end against the ledge; and a nut tightened on the first end and expanding the expandable shoulder outward on the tapered head.
 18. A method of assembling a downhole motor for a drillstring, the method comprising, not necessarily in sequence: coupling an upper portion of a motor housing to a lower portion of the motor housing; affixing a lower end of an extension to a receptacle on a distal end of a rotor disposed in the lower portion of the motor housing by— inserting a proximal end of an outer body of the extension into the receptacle of the rotor, inserting an inner body into the outer body toward an internal inward taper in a first internal passage of the outer body, and wedging the internal inward taper at the proximal end of the outer body into the receptacle of the rotor with the inserted inner body; and arranging the upper end of the extension to engage relative to a seat in the motor housing with separation of the upper and lower portions from one another.
 19. The method of claim 18, wherein inserting the inner body into the outer body comprises threading external thread on the inner body to internal thread in the first internal passage of the outer body.
 20. The method of claim 18, wherein wedging the internal inward taper at the proximal end of the outer body into the receptacle of the rotor with the inserted inner body comprises expanding a conical wedge, formed on the internal inward taper of the second end of the outer body, outward, by the inner body, into an outward taper of the receptacle on the rotor. 